JP5137923B2 - Electrode paste composition for solar cell - Google Patents

Description

  The present invention relates to a paste composition suitable for a solar cell electrode formed by a fire-through method.

For example, a general silicon-based solar cell is provided with an antireflection film and a light-receiving surface electrode on an upper surface of a silicon substrate which is a p-type polycrystalline semiconductor via an n ⁺ layer, and on the lower surface via a p ⁺ layer. It has a structure provided with electrodes (hereinafter simply referred to as “electrodes” when they are not distinguished from each other), and power generated at the pn junction of the semiconductor by light reception is taken out through the electrodes. The antireflection film is for reducing the surface reflectance and increasing the light receiving efficiency while maintaining a sufficient visible light transmittance, and is made of a thin film such as silicon nitride, titanium dioxide, or silicon dioxide.

Since the above-described antireflection film has a high electric resistance value, it prevents an electric power generated at the pn junction of the semiconductor from being efficiently extracted. Therefore, the light-receiving surface electrode of the solar cell is formed by a method called fire-through, for example. In this electrode forming method, for example, after the antireflection film is provided on the entire surface of the n ⁺ layer, a conductive paste is applied on the antireflection film in an appropriate shape by using, for example, a screen printing method, and is fired. Apply. The conductive paste is mainly composed of, for example, silver powder, glass frit (a piece of flaky or powdered glass that is crushed as necessary after melting and quenching the glass raw material), an organic vehicle, and an organic solvent. In the baking process, the glass component in the conductive paste breaks the antireflection film, so that an ohmic contact is formed by the conductive component in the conductive paste and the n ⁺ layer (for example, Patent Documents). See 1). According to the above electrode forming method, the process is simplified as compared with the case where the antireflection film is partially removed and an electrode is formed on the removed portion, and there is a problem of misalignment between the removed portion and the electrode forming position. Does not occur.

  In the formation of the light-receiving surface electrode of such a solar cell, various proposals have been made for the purpose of improving the fire-through property and improving the ohmic contact, and thus increasing the fill factor (FF) and energy conversion efficiency. It has been done. For example, by adding a Group 5 element such as phosphorus, vanadium, bismuth or the like to the conductive paste, there is one that promotes the redox action on the glass and silver antireflection film and improves the fire-through property (for example, (See Patent Document 1). In addition, by adding chloride, bromide, or fluoride to the conductive paste, these additives help the glass and silver break the antireflection film, thereby improving ohmic contact (for example, patents). See reference 2.) The glass is, for example, borosilicate glass.

In a silver-containing paste containing 85 to 99 (wt%) silver and 1 to 15 (wt%) glass, the glass was mixed with 15 to 75 (mol%) PbO and 5 to 50 (mol%) SiO. comprises _2, it is a composition that does not contain B ₂ O ₃ has been proposed (e.g., see Patent Document 3.). This silver-containing paste is used for forming an electrode of a solar cell, and the ohmic contact is improved by using the glass having the above composition.

  Further, a thick film conductive composition in which silver powder, a zinc-containing additive, and a glass frit having a softening point in a range of 300 to 600 (° C.) are dispersed in an organic solvent has been proposed (for example, a patent (Ref. 4). This thick film conductive composition is for forming a light-receiving surface electrode of a solar cell, and conductivity and solder adhesion are improved by adding zinc. For the same purpose, it has also been proposed to use a manganese-containing additive instead of the zinc-containing additive (see, for example, Patent Document 5).

Japanese Examined Patent Publication No. 03-046985 Japanese Patent No. 3707715 Special table 2008-520094 JP 2006-302890 A JP 2006-302891 A

  By the way, in the solar cell mentioned above, since a light-receiving surface electrode interrupts the incident sunlight, the energy amount which enters into a photovoltaic cell decreases according to the area which the light-receiving surface electrode occupies. On the other hand, it is conceivable to increase the light receiving area by narrowing the line width of the light receiving surface electrode. However, as the line width is decreased, it becomes difficult to obtain a good ohmic contact, and the contact resistance is increased. Since the current density decreases, the conversion efficiency decreases.

  Further, when the line width of the light-receiving surface electrode is reduced, the electrode cross-sectional area is reduced, so that the line resistance increases. It is possible to suppress the increase in resistance by reducing the amount of glass and increasing the proportion of the conductor component, but as the amount of glass decreases, the reactivity with the anti-reflection film decreases, and consequently the fire-through property decreases. As a result, the ohmic contact becomes worse.

  The present invention has been made in the background of the above circumstances, and an object thereof is to provide a solar cell electrode paste composition capable of thinning a light-receiving surface electrode without accompanying ohmic contact or deterioration of line resistance. There is.

In order to achieve such an object, the gist of the present invention is a paste composition for a solar cell electrode comprising a conductive powder, a glass frit, and a vehicle, wherein the glass frit is Li in terms of oxide. _{2 O 0.6~18 (mol%),} PbO 20~65 (mol%), B 2 O 3 1~18 (mol%), made of glass in a proportion in the range of SiO ₂ 20~65 (mol%) There is.

In this way, the solar cell electrode paste composition is composed of Li ₂ O 0.6-18 (mol%), PbO 20-65 (mol%), B ₂ O ₃ 1-18 ( mol%), SiO _{2 20 to} 65 (mol%), because it is made of glass that contains it in a range of 20% to 65% (mol%). Even if the line width is reduced, a good ohmic contact can be obtained. In addition, since the paste composition of the present invention has excellent fire-through properties, the amount of glass can be reduced while maintaining good ohmic contact, so that there is an advantage that the line resistance of the light-receiving surface electrode can be further reduced. . Therefore, according to the solar cell electrode paste composition of the present invention, the light-receiving surface electrode can be thinned without accompanying ohmic contact or line resistance deterioration. As a result, even if the line is thinned and the light receiving area is increased, the contact resistance is sufficiently low, so that the fill factor does not decrease, so that a solar cell with high photoelectric conversion efficiency can be obtained.

  In addition, since thinning is possible as described above, there is an advantage that it can be suitably used for a shallow emitter having a high sheet resistance. Incidentally, the shallow emitter has an n-layer thickness on the light-receiving surface side of 70 to 100 (nm), which is thinner than the conventional silicon solar cell 100 to 200 (nm). Among them, since the portion that cannot be effectively used by changing to heat before reaching the pn junction is reduced, there is an advantage that the short circuit current is increased and the power generation efficiency is increased. However, since the donor element concentration generally decreases, the barrier barrier between Ag and Si increases, and the contact resistance increases. The said composition glass can fully contain a donor element and can make contact resistance low. On the other hand, since the n layer is thin, it is necessary to more strictly control the electrode formation by fire-through. However, since the electrode paste composition of the present invention contains the glass of the above composition, erosion control is easy. .

  In the glass frit composition, PbO is a component that lowers the softening point of glass and is a component that enables low-temperature firing, and PbO is 20 (mol%) or more in order to obtain good fire-through properties. And it is necessary to be 65 (mol%) or less. If the amount of PbO is less than 20 (mol%), the softening point becomes too high, so that it is difficult to erode the antireflection film, and good ohmic contact cannot be obtained. On the other hand, if it exceeds 65 (mol%), the softening point becomes too low, so that the erosion becomes too strong and the pn junction is broken. The amount of PbO is more preferably 22.4 (mol%) or more, and further preferably 50.8 (mol%) or less. That is, the range of 22.4 to 50.8 (mol%) is more preferable. Moreover, about 30-40 (mol%) is especially preferable.

B ₂ O ₃ is a glass-forming oxide (that is, a component that forms a glass skeleton), and is a component for lowering the softening point of glass. To obtain good fire-through properties, B ₂ O ₃ Is required to be 1 (mol%) or more and 18 (mol%) or less. If the amount of B ₂ O ₃ is less than 1 (mol%), the softening point becomes too high and it becomes difficult to erode into the antireflection film, and as a result, a good ohmic contact cannot be obtained and the moisture resistance also decreases. In particular, in the present invention, since Li is contained in the glass, it is extremely difficult to melt unless 1 (mol%) or more of B ₂ O ₃ is contained. On the other hand, if it exceeds 18 (mol%), the softening point becomes too low, so that the erosion becomes too strong and the pn junction is broken. The amount of B ₂ O ₃ is more preferably 2.8 (mol%) or more, and further preferably 12 (mol%) or less. That is, the range of 2.8 to 12 (mol%) is more preferable. Moreover, about 6-12 (mol%) is especially preferable.

In addition, SiO ₂ is a glass-forming oxide, a component for increasing the chemical resistance of the glass, SiO ₂ is 20 (mol%) or more and 65 (mol%) in order to obtain good fire-through properties ) It must be: If the amount of SiO ₂ is less than 20 (mol%), chemical resistance is insufficient and glass formation becomes difficult.On the other hand, if it exceeds 65 (mol%), the softening point becomes too high and it is difficult to erode the antireflection film. As a result, a good ohmic contact cannot be obtained. The amount of SiO ₂ is more preferably 27.0 (mol%) or more, and further preferably 48.5 (mol%) or less. That is, the range of 27.0 to 48.5 (mol%) is more preferable. Moreover, about 30-35 (mol%) is especially preferable.

Li ₂ O is a component that lowers the softening point of glass, and Li ₂ O must be 0.6 (mol%) or more and 18 (mol%) or less in order to obtain good fire-through properties. It is. If Li ₂ O is less than 0.6 (mol%), the softening point becomes too high and the erosion property to the antireflection film becomes insufficient. On the other hand, if it exceeds 18 (mol%), the erodibility becomes too strong, and the electrical characteristics deteriorate. Incidentally, Li is generally an impurity for semiconductors because it promotes diffusion, and Li tends to deteriorate the characteristics, so it is desirable to avoid it in semiconductor applications. In particular, when the amount of Pb is usually large and Li is contained, the erodibility tends to be too strong and control tends to be difficult. However, in the solar cell application as described above, no deterioration in characteristics was observed using glass containing Li, and on the other hand, an appropriate amount was included, thereby improving the fire-through property and improving the characteristics. Li is a donor element and can reduce contact resistance. In addition, it was recognized that the composition range of the glass capable of obtaining good fire-through properties was increased by adopting a composition containing Li. However, even in solar cell applications, if it is excessively contained, the erodibility becomes too strong, and the electrical characteristics tend to deteriorate. The amount of Li ₂ O is more preferably 6 (mol%) or more, and further preferably 12 (mol%) or less. That is, the range of 6 to 12 (mol%) is more preferable. Further, about 6 (mol%) is particularly preferable.

  Incidentally, Patent Documents 4 and 5 describe lead glass containing a very small amount of Li of 0.1 (wt%) or less (= 0.58 (mol%) or less). That is, it is also described that glass containing Li can be used for the electrode paste composition. However, these do not describe any advantage of including Li, nor does it indicate a reason for the content to be 0.1 (wt%) or less. On the other hand, the present inventors have unexpectedly improved the fire-through property by using a glass containing a large amount of Li to the extent that it has been thought that it has been conventionally unacceptable as described above, and the electrode pattern It has been found that a good ohmic contact can be obtained even if the wire is thinned, and the present invention has been made based on such knowledge.

  In addition, although it is difficult to specify in which form each of the above components is contained in the glass, these ratios are all values converted to oxides.

  In addition, the glass constituting the electrode paste of the present invention may contain other various glass components and additives as long as the properties are not impaired. For example, Al, Zr, Na, Ca, Zn, Mg, K, Ti, Ba, Sr, etc. may be contained. Since Al is an effective component for obtaining the stability of the glass, it hardly affects the properties but is preferably contained. These may be included in a total range of 30 (mol%) or less, for example. For example, Al and Ti are each preferably 6 (mol%) or less, and more preferably 3 (mol%) or less. Zn is preferably 30 (mol%) or less, and more preferably 15 (mol%) or less. By using a composition containing appropriate amounts of these Al, Ti, and Zn, the parallel resistance Rsh is improved, and the open-circuit voltage Voc and the short-circuit current Isc are improved, so that higher electrical characteristics can be obtained.

  Here, preferably, the glass frit has an average particle diameter (D50) in the range of 0.3 to 3.0 (μm), and is contained in a ratio in the range of 1 to 20 (vol%) with respect to the entire paste. Is. If the average particle size of the glass frit is too small, melting will be too early when the electrode is fired, resulting in a decrease in electrical characteristics, but if it is 0.3 (μm) or more, moderate melting properties can be obtained, so that the electrical characteristics are further enhanced. . In addition, since agglomeration is unlikely to occur, better dispersibility can be obtained during paste preparation. Also, the dispersibility of the entire powder is lowered when the average particle size of the glass frit is significantly larger than the average particle size of the conductive powder, but better dispersibility can be obtained when it is 3.0 (μm) or less. Moreover, a further melting property of the glass can be obtained. In addition, if the glass amount is 1 (vol%) or more, the melting property of the antireflection film is further improved, so that a better ohmic contact can be obtained. Further, if the amount of glass is 20 (vol%) or less, it is difficult to form a single insulating layer, so that higher conductivity can be obtained. Therefore, in order to obtain a better ohmic contact, it is preferable to satisfy both the average particle diameter and the ratio in the paste. The ratio in the paste is particularly preferably 2 to 10 (vol%).

  The average particle size of the glass frit is a value obtained by the air permeation method. The air permeation method is a method for measuring the specific surface area of a powder from the permeability of a fluid (for example, air) to a powder layer. The basis of this measurement method is the Kozeny-Carmann equation, which shows the relationship between the wetted surface area of all particles constituting the powder layer and the flow velocity and pressure drop of the fluid passing therethrough. The specific surface area of the sample is obtained by measuring the flow velocity and pressure drop with respect to the powder layer filled under the conditions determined by the above. In this method, the gap between the filled powder particles is regarded as pores, and the wetted surface area of the particles that resists the flow of air is determined. Usually, the value is smaller than the specific surface area determined by the gas adsorption method. Show. An average particle diameter assuming powder particles can be calculated from the obtained specific surface area and particle density.

  Preferably, the conductive powder is a silver powder having an average particle diameter (D50) in the range of 0.3 to 3.0 (μm). Although copper powder, nickel powder, etc. can be used as the conductive powder, silver powder is most preferable in order to obtain high conductivity. Further, if the average particle size of the silver powder is 3.0 (μm) or less, better dispersibility can be obtained, and thus higher conductivity can be obtained. Moreover, if it is 0.3 (μm) or more, aggregation is suppressed and better dispersibility can be obtained. Since silver powder of less than 0.3 (μm) is extremely expensive, 0.3 (μm) or more is preferable from the viewpoint of manufacturing cost. Further, if the average particle diameter of both the conductive powder and the glass frit is 3.0 (μm) or less, there is an advantage that clogging hardly occurs even when the electrode is printed by a fine line pattern.

  The silver powder is not particularly limited, and enjoys the basic effect of the present invention that thinning can be achieved while maintaining conductivity even when a powder of any shape such as a spherical shape or a scale shape is used. Can do. However, when the spherical powder is used, the printability is excellent and the filling rate of the silver powder in the coating film is increased, so that, together with the use of highly conductive silver, other shapes such as scales are used. Compared with the case where the silver powder of this is used, the electrical conductivity of the electrode produced | generated from the coating film becomes high. Therefore, it is particularly preferable because the line width can be further reduced while ensuring the necessary conductivity.

  Also preferably, the solar cell electrode paste composition has a viscosity at 25 (° C.)-20 (rpm) in the range of 150 to 250 (Pa · s), a viscosity ratio (ie, 10 (rpm)). Viscosity / viscosity at 100 (rpm)) is 3-8. By using a paste having such a viscosity characteristic, the viscosity is suitably reduced during squeezing and transmitted through the screen mesh. After the transmission, the viscosity returns to a high viscosity and the expansion of the printing width is suppressed. Thus, a fine line pattern can be easily obtained while maintaining the printability such that clogging does not easily occur and clogging does not occur. The viscosity of the paste composition is more preferably in the range of 160 to 200 (Pa · s), and the viscosity ratio is more preferably in the range of 3.2 to 6.0. In addition, a viscosity ratio of 4 to 6 is desirable for thinning a design line width of 100 (μm) or less.

  Note that increasing the film thickness so that the cross-sectional area can be maintained even if the line width is reduced includes, for example, increasing the emulsion thickness of the printing plate, increasing the tension, and reducing the line diameter. It is also possible to widen the aperture. However, when the emulsion thickness is increased, the separation of the plate is deteriorated, so that the stability of the printed pattern shape cannot be obtained. In addition, when the tension is increased or the wire diameter is reduced, the screen mesh is easily stretched, so that it is difficult to maintain the dimensional and shape accuracy and the durability of the printing plate making is lowered. In addition, since it is provided with a large width, a bus bar that is unnecessary to increase the film thickness is also increased, resulting in a problem of waste of material.

  Preferably, the paste composition for a solar cell electrode includes the conductive powder in a proportion in the range of 64 to 90 parts by weight and the vehicle in a range of 3 to 20 parts by weight. In this way, a paste composition can be obtained that can easily form an electrode having good printability, thin line width, and high conductivity.

  In addition, since the conductive composition of the present invention can suitably control the diffusion of silver during the electrode formation by fire-through as described above, it can be suitably used for the light-receiving surface electrode.

Further, the glass frit can be synthesized from various raw materials that can be vitrified within the composition range, and examples thereof include oxides, carbonates, nitrates, etc. Examples of the Si source include silicon dioxide SiO _2. As a B source, boric acid B ₂ O ₃ can be used, and as a Pb source, red lead Pb ₃ O ₄ can be used.

  Moreover, when it is set as the composition containing other components, such as Al and Zr, in addition to main components Si, B, and Pb, those oxides, hydroxides, carbonates, nitrates etc. may be used, for example.

It is a schematic diagram which shows the cross-sectional structure of the solar cell with which the paste composition for electrodes of one Example of this invention was applied for formation of a light-receiving surface electrode. It is a figure which shows an example of the light-receiving surface electrode pattern of the solar cell of FIG.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

FIG. 1 is a diagram schematically showing a cross-sectional structure of a silicon-based solar cell 10 to which a conductive composition according to an embodiment of the present invention is applied. In FIG. 1, a solar cell 10 includes a silicon substrate 12 which is, for example, a p-type polycrystalline semiconductor, an n layer 14 and a p ⁺ layer 16 respectively formed on the upper and lower surfaces thereof, and a reflection formed on the n layer 14. A prevention film 18 and a light-receiving surface electrode 20 and a back electrode 22 formed on the p ⁺ layer 16 are provided. The thickness dimension of the silicon substrate 12 is, for example, about 100 to 200 (μm).

The n layer 14 and the p ⁺ layer 16 are provided by forming layers having a high impurity concentration on the upper and lower surfaces of the silicon substrate 12, and the thickness dimension of the high concentration layer is, for example, 70% for the n layer 14. ˜100 (nm), and the p ⁺ layer 16 is about 500 (nm), for example. The n layer 14 is about 100 to 200 (nm) in a general silicon solar cell, but is thinner than that in this embodiment, and has a structure called a shallow emitter. The impurity contained in the n layer 14 is an n-type dopant such as phosphorus (P), and the impurity contained in the p ⁺ layer 16 is a p-type dopant such as aluminum (Al) or boron (B). .

The antireflection film 18 is a thin film made of, for example, silicon nitride Si ₃ N ₄ , and is provided with an optical thickness of, for example, about ¼ of the visible light wavelength, for example, about 80 (nm). It is configured to have an extremely low reflectance of 10 (%) or less, for example, 2 (%).

The light-receiving surface electrode 20 is made of, for example, a thick film conductor having a uniform thickness. As shown in FIG. 2, the light-receiving surface electrode 20 is a comb having a large number of thin line portions substantially on the entire surface of the light-receiving surface 24. Are provided in a planar shape. The above thick film conductor has a Ag in the range of 67 to 98 (wt%), for example, about 94.3 (wt%), and a glass in the range of 2 to 33 (wt%), for example, about 5.7 (wt%). made of a thick film silver containing, a value that the glass in terms oxides, in the range of 20-65 and PbO (mol%), for example, 39 (mol%) of about, B ₂ O ₃ and 1 to 18 (mol in the range of%), for example 12.0 (mol%) or so, the range of SiO ₂ and 20 to 65 (mol%), for example 31.0 (mol%) or so, in the range of 0.6 to 18 and Li ₂ O (mol%) , for example 6.0 (mol%) or so, in the range of Al ₂ O ₃ and Less than six (mol%), for example, 3 (mol%) or so, the TiO ₂ in the range of Less than six (mol%), for example, 3 ( lead glass containing ZnO at a rate of about 6 (mol%), for example, within a range of 0 to 30 (mol%), for example, ZnO. In addition, the thickness dimension of the conductor layer is, for example, in the range of 20-30 (μm), for example, about 25 (μm), and the width dimension of each thin line portion is in the range of, for example, 80-130 (μm) It is about 100 (μm) and has sufficiently high conductivity.

The back electrode 22 is formed by applying a full-surface electrode 26 formed by applying a thick film material containing aluminum as a conductor component on the p ⁺ layer 16 over almost the entire surface, and a strip-like application on the full-surface electrode 26. The band-shaped electrode 28 made of thick film silver is formed. The belt-like electrode 28 is provided in order to make it possible to solder a conducting wire or the like to the back electrode 22.

In the solar cell 10 of this example, the light-receiving surface electrode 20 has PbO in the range of 20 to 65 (mol%), B ₂ O ₃ in the range of 1 to 18 (mol%), and SiO ₂ as described above. 20-65 in the range of (mol%), in the range of 0.6 to 18 and Li ₂ O (mol%), in the range of Al ₂ O ₃ to 0~6 (mol%), TiO ₂ and Less than six (mol %) And ZnO in a proportion within the range of 0-30 (mol%), respectively, and lead glass composition containing lead glass with a thickness of 2-33 (wt%). Therefore, although the line width is reduced to about 100 (μm), a good ohmic contact with the n layer 14 is obtained, and the contact resistance is low.

  In addition, since the light receiving surface electrode 20 of the present embodiment has high conductivity because the glass amount is as small as about 5.7 (wt%) as described above, the film thickness and the line width are any. Although the line resistance is low, the photoelectric conversion efficiency of the solar cell 10 is enhanced in combination with the low contact resistance.

  The light receiving surface electrode 20 as described above is formed by, for example, a well-known fire-through method using an electrode paste made of conductive powder, glass frit, vehicle, and solvent. An example of the manufacturing method of the solar cell 10 including the formation of the light receiving surface electrode will be described below.

First, the glass frit is produced. Lithium carbonate Li ₂ CO ₃ as Li source, silicon dioxide SiO ₂ as Si source, boric acid B ₂ O ₃ as B source, red lead Pb ₃ O ₄ as Pb source, aluminum oxide as Al source Al ₂ O ₃ Are prepared by preparing titanium oxide TiO ₂ as a Ti source and zinc oxide ZnO as a Zn source, respectively, and weighing and preparing so as to have an appropriate composition within the above-mentioned range. This is put into a crucible, melted at a temperature in the range of 900 to 1200 (° C.) according to the composition for about 30 minutes to 1 hour, and rapidly cooled to be vitrified. This glass is pulverized using an appropriate pulverizing apparatus such as a planetary mill or a ball mill. The average particle size (D50) after pulverization is, for example, about 0.3 to 3.0 (μm).

  On the other hand, as the conductor powder, for example, a commercially available spherical silver powder having an average particle diameter (D50) in the range of 0.3 to 3.0 (μm) is prepared. By using such silver powder having a sufficiently small average particle diameter, the filling rate of the silver powder in the coating film can be increased and the electrical conductivity of the conductor can be increased. The vehicle is prepared by dissolving an organic binder in an organic solvent. For example, butyl carbitol acetate is used as the organic solvent, and ethyl cellulose is used as the organic binder. The ratio of ethyl cellulose in the vehicle is, for example, about 15 (wt%). A solvent added separately from the vehicle is, for example, butyl carbitol acetate. That is, although it is not limited to this, the same solvent as that used for the vehicle may be used. This solvent is added for the purpose of adjusting the viscosity of the paste.

  Prepare the above paste raw materials, for example, conductor powder 77-88 (wt%), glass frit 1-10 (wt%), vehicle 7-14 (wt%), solvent 3-5 (wt %) And are mixed using a stirrer or the like, and then subjected to a dispersion treatment using, for example, a three-roll mill. Thereby, the electrode paste is obtained.

While preparing the electrode paste as described above, the n layer 14 and the p ⁺ layer are diffused or implanted into an appropriate silicon substrate by a well-known method such as a thermal diffusion method or ion plantation. By forming 16, the silicon substrate 12 is produced. Next, a silicon nitride thin film is formed thereon by an appropriate method such as PE-CVD (plasma CVD), and the antireflection film 18 is provided.

  Next, the electrode paste is screen-printed on the antireflection film 18 with the pattern shown in FIG. This is dried at, for example, 150 (° C.), and further subjected to a baking treatment at a temperature in the range of 740 to 900 (° C.) in a near infrared furnace. As a result, the glass component in the electrode paste melts the antireflection film 18 in the firing process, and the electrode paste breaks the antireflection film 18, so that the conductor component in the electrode paste, that is, silver and the n layer 14 Electrical connection is obtained, and an ohmic contact between the silicon substrate 12 and the light-receiving surface electrode 20 is obtained as shown in FIG. The light receiving surface electrode 20 is formed in this way.

  In addition, although the said back surface electrode 22 may be formed after the said process, it can also be formed by baking simultaneously with the light-receiving surface electrode 20. FIG. When the back electrode 22 is formed, the entire surface electrode 26 made of a thick aluminum film is formed by applying, for example, an aluminum paste to the entire back surface of the silicon substrate 12 by screen printing or the like and performing a baking process. Further, the strip electrode 28 is formed by applying the electrode paste on the surface of the entire surface electrode 26 in a strip shape using a screen printing method or the like and performing a baking treatment. Thereby, the back electrode 22 which consists of the full surface electrode 26 which covers the whole back surface, and the strip | belt-shaped electrode 28 provided in strip shape on a part of the surface is formed, and the said solar cell 10 is obtained. In the above process, when manufacturing by simultaneous firing, a printing process is performed before firing the light-receiving surface electrode 20.

  Various changes were made to the glass composition, the solar cell 10 was produced according to the above production process, the output was measured using a commercially available solar simulator, and the curve factor FF value was evaluated. Shown in In Table 1, No. 1 to 4, 6 to 24, 26 to 29, 32 to 38, 41, 42, 44, 45, 47 to 50, 53 to 56, 58 to 63, 65 to 72, 74 to 91, Examples 93 to 97, 99, and 100 are examples, and others are comparative examples. In general, a solar cell can be used if the FF value is 70 or more, but it is of course preferable that the solar cell is higher. In this example, a solar cell having an FF value greater than 75 was accepted.

  Each sample was prepared using spherical Ag powder having an average particle size of 1.6 (μm) and glass frit having an average particle size of 1.5 (μm). The mixing ratio is based on Ag powder 83 (wt%), glass frit 5 (wt%), vehicle 8 (wt%), solvent 5 (wt%), and 20 (° C) − The amount of vehicle and the amount of solvent were adjusted so that the viscosity at 20 (rpm) was 160 to 180 (Pa · s). Further, the printing plate making for forming the light-receiving surface electrode 20 was made by providing a 20 (μm) emulsion on a SUS325 screen mesh having a wire diameter of 23 (μm). The printing conditions were set so that the width of the grid line was 100 (μm).

In Table 1, as an _{example, PbO-B 2 O 3 -SiO} 2 -Li 2 O 4 component _{system, PbO-B 2 O 3 -SiO} 2 -Li 2 5 -component of the O-ZnO, PbO B ₂ O ₃ —SiO ₂ —Li ₂ O—Al ₂ O ₃ ternary system, PbO—B ₂ O ₃ —SiO ₂ —Li ₂ O—TiO ₂ ternary system, PbO—B ₂ O ₃ —SiO ₂ -Li ₂ O-TiO ₂ -ZnO six component system, 7-component system _{PbO-B 2 O 3 -SiO 2} -Al 2 O 3 -Li 2 O-TiO 2 -ZnO is shown. Examples Nos. 1 to 4, 20 to 24, 26 to 29, 38, 41, 42, 44, 45, 47 to 50, 53 to 56 are quaternary systems, but PbO is 20.0 to 65.0 (mol%). ), B ₂ O ₃ was 1.0 to 18.0 (mol%), SiO ₂ was 20.0 to 65.0 (mol%), Li ₂ O was 0.6 to 18.0 (mol%), and an FF value exceeding 75 was obtained. . In this four-component system, looking at a comparative example, the FF values stayed at 63 and 70 in Nos. 5 and 39, respectively, where Li ₂ O was as high as 24.0 (mol%). It is thought that when Li ₂ O is excessive, the erosion property becomes too strong during firing for electrode formation. Further, No. 25 having a low Li ₂ O of 0.4 (mol%) also had an FF value of 73. Moreover, the FF value stayed at 73 or less even with Nos. 30, 31, 51 and 57 with B ₂ O ₃ of 19.0 (mol%) or more. When these Examples and Comparative Examples are compared, in a four-component system, Li ₂ O is 0.4 (mol%) or less or 24.0 (mol%) or more, or B ₂ O ₃ is 19.0 (mol%) or more. Then, it can be seen that the characteristics cannot be obtained.

In Examples, Nos. 12, 13, 32, and 33 are five-component systems containing Al ₂ O ₃ , in which PbO is 30.0 to 45.6 (mol%), and B ₂ O ₃ is 3.0 to 5.0 (mol). %), SiO ₂ 35.0 to 49.0 (mol%), Al ₂ O ₃ 3.0 to 6.0 (mol%), Li ₂ O 12.0 (mol%), and FF values exceeding 75 are all obtained. It was.

In Examples, Nos. 14, 15, 34, and 35 are ternary systems containing TiO ₂ , in which PbO is 30.0 to 45.6 (mol%) and B ₂ O ₃ is 3.0 to 5.0 (mol%). , SiO ₂ is _{35.0~49.0 (mol%), Li 2} O is 12.0 (mol%), TiO ₂ is in the range of 3.0~6.0 (mol%), both FF value exceeding 75 was obtained.

Further, Nos. 6 to 11, 16 to 19, 36, 37, 58 to 63 in Examples are five-component systems containing ZnO. In this system, PbO is 30.0 to 49.0 (mol%), and B ₂ O ₃ is 3.0~12.0 (mol%), SiO ₂ is _{24.4~49.0 (mol%), Li 2} O is 6.0~12.0 (mol%), ZnO is in the range of 3.0~30.0 (mol%), both exceeding 75 FF A value was obtained.

Examples Nos. 79 to 82, 93 to 96, and 100 are six-component systems containing Li ₂ O, TiO ₂ , and ZnO, that is, systems that do not contain Al ₂ O _{3. 25.9~42.3 (mol%), B 2} O 3 is 6.0~12.0 (mol%), SiO ₂ is _{24.4~41.1 (mol%), Li 2} O is 6.0~12.0 (mol%), TiO ₂ is 6.0 (mol %), ZnO was in the range of 6.0 to 15.0 (mol%), and FF values exceeding 75 were obtained in all cases.

Further, Nos. 65 to 72, 74 to 78, and 83 to 91 in the examples are 7-component systems including all of Al ₂ O ₃ , Li ₂ O, TiO ₂ , and ZnO, but PbO is 22.4 to 45 (mol). %), B ₂ O ₃ is 3.0 to 18.0 (mol%), SiO ₂ is 21.7 to 41.1 (mol%), Al ₂ O ₃ is 3.0 (mol%), Li ₂ O is 0.6 to 18.0 (mol%), FF values exceeding 75 were obtained in the range of TiO ₂ of 3.0 (mol%) and ZnO of 6.0 to 15.0 (mol%). Looking at the comparative example in this 7-component system, the FF value is No. 73 and 92 where B ₂ O ₃ is as high as 19 (mol%) or more, and No. 64 where Li ₂ O is as low as 0.4 (mol%). Stayed below 73.

Moreover, the FF value is small in the three-component system lacking Li ₂ O like No. 40 and 43 in the comparative example, and especially, No. 40 having a large Si amount of 68 (mol%) has an extremely low FF value of 38. It was a result. Further, the FF value of the three-component system lacking B ₂ O ₃ as well as the comparative examples Nos. 46 and 52 remained below 75.

According to the evaluation result of this example shown in Table 1 above, even when the line width of the light-receiving surface electrode 20 is reduced to about 100 (μm) by using a glass frit having a composition within the above-described range, FF values exceeding 75 are obtained. As described above, an excellent fire-through property can be obtained even with a small glass amount of about 5 (wt%) with respect to the entire paste, and a good ohmic contact can be obtained. This is considered to be because thinning is possible and the effect of increasing the light receiving area can be suitably enjoyed. That is, in the paste composition of this example, the glass frit is Li ₂ O 0.6-18 (mol%), PbO 20-65 (mol%), B ₂ O ₃ 1-18 (mol%), SiO ₂ 20- Since it is made of glass containing at a ratio in the range of 65 (mol%), an excellent fire-through property can be obtained when the light-receiving surface electrode 20 is formed by coating on the antireflection film 18, so that the line width is reduced. However, a good ohmic contact can be obtained. As a result, the amount of glass can be reduced while maintaining a good ohmic contact, so that the line resistance of the light-receiving surface electrode 20 can be further reduced. Therefore, the light-receiving surface electrode 20 can be thinned without accompanying ohmic contact or deterioration of line resistance. Therefore, even if the light-receiving area is increased by thinning, the contact resistance is sufficiently low, so the FF value does not decrease. The solar cell 10 with high photoelectric conversion efficiency is obtained.

Further, according to the results shown in Table 1 above, for example, if the composition contains a large amount of Li ₂ O of 3 (mol%) or more, excellent fire-through properties can be obtained with a wide range of glass compositions, and consequently photoelectric conversion. It turns out that the paste composition for electrodes which can manufacture the solar cell 10 with high efficiency is obtained.

  Table 2 below provides Ag powders with different average particle sizes in the range of 0.3 to 3.0 (μm), and the average particle size of the glass frit is also changed in the range of 0.3 to 4.0 (μm). The results of preparing the paste and forming the light-receiving surface electrode 20 to evaluate the characteristics of the solar cell 10 are summarized. In the Ag powder column, A to F represent the types of silver powder, and the average particle sizes are 3.0 (μm) for A, 2.2 (μm) for B, 1.6 (μm) for C, and 0.8 (μm) for D, respectively. E is 0.5 (μm) and F is 0.3 (μm). The frit numbers in the glass column correspond to the sample numbers shown in Table 1 above. The number in the leftmost column is a combination of the Ag powder type and the frit number. The same combinations with different glass average particle diameters were distinguished by attaching branch numbers. Conditions not specifically shown are the same as those shown in Table 1.

  As shown in the above evaluation results, in the sample of A69 to F69 using the No. 69 frit, the Ag powder particle size is 0.3 to 3.0 (μm) in the whole range, 75 without changing the formulation specification. An FF value exceeding 1 was obtained. At least in the evaluated range, the particle size of the Ag powder is not particularly limited, and any particle size of 0.3 to 3.0 (μm) can be used.

In addition, the samples C69-1 to C68 using Ag powder C are obtained by variously changing the type and particle size of the glass frit. When any of the glass frit Nos. 68, 69, 78, and 98 is used. In addition, an FF value exceeding 75 was obtained. C69-1 and C69-2 have the same glass composition and particle sizes of 0.8 (μm) and 3.0 (μm). Results were obtained. In addition, C98-1 and C68 increased the amount of vehicle for the purpose of adjusting the viscosity. However, like other samples, the light-receiving surface electrode 20 can be formed with a line width of 100 (μm), and an FF value exceeding 75 is obtained. I was able to. In C78-1, good results were obtained even when the glass content was 1 (wt%). By making a glass composition containing a large amount of, for example, 6.0 (mol%) Li ₂ O, the erosion property is enhanced, so that a good ohmic contact can be obtained even with a small amount of glass, and the line resistance is also low. Conceivable.

  In addition, the F98 sample was obtained by changing only the glass frit with respect to the F69 sample. That is, no particular effect was observed due to the difference in glass type.

  Further, C69-3, C69-4 confirmed the upper and lower limits of the glass particle size, but when frit No. 69 was used after pulverized to an average particle size of 0.3 (μm), 1 ( FF value exceeding 75 was obtained with the blending amount of wt%). On the other hand, when the powder was pulverized to 4.0 (μm), the FF value remained at about 70 as the blending amount of 5 (wt%).

  According to the above results, the particle size of Ag powder is not particularly limited, and the glass type is not particularly limited as long as it is within the range of the examples shown in Table 1, but the average particle size is preferably 3.0 (μm) or less. It can be said.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

For example, in the above embodiment, the antireflection film 18 is made of a silicon nitride film. However, the constituent material is not particularly limited, and various other materials such as titanium dioxide TiO ₂ generally used for solar cells. Those consisting of can be used as well.

  In the embodiments, the case where the present invention is applied to the silicon-based solar cell 10 has been described. However, the present invention is applicable to any solar cell in which the light-receiving surface electrode can be formed by the fire-through method. The substrate material is not particularly limited.

10: solar cell, 12: silicon substrate, 14: n layer, 16: p ⁺ layer, 18: antireflection film, 20: light receiving surface electrode, 22: back electrode, 24: light receiving surface, 26: full surface electrode, 28: Strip electrode

Claims (3)

A solar cell electrode paste composition comprising a conductive powder, a glass frit, and a vehicle,
The glass frit is Li ₂ O 0.6-18 (mol%), PbO 20-65 (mol%), B ₂ O ₃ 1-18 (mol%), SiO ₂ 20-65 (mol%) in terms of oxide. A paste composition for a solar cell electrode, comprising a glass contained in a proportion within the range.   The glass frit has an average particle size (D50) in the range of 0.3 to 3.0 (μm), and is contained in a proportion in the range of 1 to 20 (vol%) with respect to the entire paste. A paste composition for a solar cell electrode.   The solar cell electrode paste composition according to claim 1 or 2, wherein the conductive powder is a silver powder having an average particle size (D50) in the range of 0.3 to 3.0 (µm).

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